This invention relates to a valve actuation system for independently actuating each of the valves associated with the flow passages in a regenerative thermal oxidizer.
Regenerative thermal oxidizers ("RTOs") are used to remove pollutants from an industrial gas stream. In particular, RTOs are often utilized to remove volatile organic compounds from a gas stream. In a basic RTO structure, several heat exchangers are each communicated with a common combustion chamber. Each of the heat exchangers receives at least an inlet passage and an outlet passage. The several inlet passages are all connected to an inlet manifold, and the several outlet passages are all connected to an outlet manifold. Valves are placed on each inlet passage and each outlet passage. A supply of air to be cleaned is communicated through the inlet manifold, and the inlet valve on one of the inlet passages is opened to allow the flow of that air through the heat exchanger and into the combustion chamber. The air typically carries pollutants and will be referred to as "dirty" air for purposes of this application. At the same time, cleaned air from the combustion chamber passes through a second of the heat exchangers through an open outlet valve and to the outlet manifold. The valves are cyclically moved between their respective heat exchangers being in an inlet mode and in an outlet mode to continuously process dirty gas.
The air passing through inlet passage, the heat exchanger and into the combustion chamber is heated by the previously heated heat exchanger elements. The cool air to be cleaned cools the heat exchanger. The hot air leaving the combustion chamber heats the previously cooled heat exchanger, thus reheating the heat exchanger for use to heat the air to be cleaned in the next cycle.
Problems exist in properly timing the opening and closing of the several valves. While pneumatic or electronic valve actuation controls have been utilized in these systems, the inherent unreliability in such controls has let to problems. In particular, one must ensure that the inlets and outlet valves are never commonly opened on any one heat exchanger. If both valves were opened on any one heat exchanger, dirty air could flow from the inlet manifold directly to the outlet manifold. The outlet manifold is typically connected to atmosphere, and the connection of the dirty air to be cleaned to the outlet manifold is undesirable.
Mechanical valve actuation systems have been used that typically utilized a single cam member controlling the valves for each of the several heat exchangers. The prior art mechanical valve controls for an RTO system have typically been limited due to the use of a single cam to actuate each of the valves. The single cam reduces the ability to vary the opening and closing of the valves relative to each other. In some applications it may be desirable to change the respective opening and closing times of the valve between the inlet and outlet valves. The prior art mechanical valve actuation systems have not provided sufficient flexibility in this regard.
In the prior art, the single cam has been used, since it has been thought necessary to ensure that the valves are never improperly opened, leading to a leakage situation. However, the use of the single cam puts severe restrictions on the arrangements of the flow passages leading from both the inlet and outlet manifolds.
In another problem with existing RTO systems, impurities will sometimes liquify out of the gas stream. In particular, contaminants such as resins or plasticizers are often found in the dirty air to be cleaned. These substances will often begin in the vapor form, but condense as the temperature drops on the way to the RTO system. In particular, these substances will often become a liquid as they enter the inlet manifold and head towards the inlet passage. The liquid tends to coat the inside walls of the inlet manifold duct work and is carried into the inlet valves. Once these impurities pass the inlet valves, they enter the heat exchanger and are revolatilized by the hot temperatures in the heat exchange chamber. However, prior to the impurities reaching the inlet valves, a problem is created in that the substances in their liquid state coat the manifold and cause a potential fire hazard and housing cleaning problem. Further, when the impurities coat the inlet valve seats, they may harden. The hardened impurities can create a crust along the inlet valve disk/valve seat interface, such that the valve disk will not fully close. This can result in leakage across the valve disk, which is undesirable.
In another problem in present RTO systems, it is desirable to ensure that a purge valve is not open unless the inlet valve is closed along with the outlet valve. In some prior systems, it has been possible to open the inlet and purge valve for a common period of time. With the increase in cost of fuel, this common opening has proven to be too inefficient for practical application.